Step 1Cut the red onions into one-eighth-inch-thick slices. Set aside.
Step 2In a medium bowl, whisk together the red wine vinegar, sugar, salt and pepper, making sure everything is dissolved
Step 3In a medium-sized heavy-bottomed pot, combine the onions and vinegar mixture. Cook over high heat, stirring occasionally, until the mixture is reduced by half and the onions are softened, light pink to purple in color and slightly translucent, about 30 minutes. Pour the mixture into a shallow glass baking dish and cool before using. This makes about 2 cups of Howie red onions.
Step 1In a medium bowl, whisk together the light brown sugar, Worcestershire sauce, heavy cream and ground black pepper. Mix in the Dijon mustard and mayonnaise. This makes about 2 2/3 cups Dijonnaise, more than is needed for the remainder of the recipe. The Dijonnaise will keep, covered and refrigerated, up to 1 week.
Step 1Heat a grill over medium-high heat until hot. Grill the burgers to desired doneness, about 2 to 4 minutes on each side for medium.
Step 2Just before pulling the burgers off the grill, top each patty with one-half cup Howie onions. Place 2 slices Gruyere over the onions and continue cooking until the cheese is fully melted. Remove and set aside in a warm place.
Step 3Toast the buns on the grill, and slather the top half of each with a scant 3 tablespoons Dijonnaise. Place about 1 cup shredded lettuce on the bottom of each toasted bun, place the burger on top and then cover with the top of the bun. Serve immediately.